The present invention relates to a failure detecting system for an automatic transmission of a vehicle employing an engine rotational speed, a cruise control signal, a brake signal from a brake switch or a shift range switch operation signal from a shift range switch as one of control signals to control the automatic transmission.
An automatic transmission AT is fundamentally controlled to be shifted by regulating depression of an accelerator pedal and a traveling speed of a vehicle. Accordingly, in case where the vehicle travels in a drive (D) range, reduction gears can be shifted by positively depressing or releasing the accelerator pedal.
In a conventional automatic transmission, for example, in a drive (D) range, an optimum gear is selectively controlled from a vehicle speed at that time and a throttle opening according to a shift map storing a predetermined shift schedule as shown in FIG. 14.
As a lockup function of an automatic transmission a lockup clutch is engaged when a vehicle speed becomes higher than a predetermined value in a certain gear position such as, for example, in a third gear or an overdrive (fourth gear), to directly couple an output shaft of a torque converter to an output shaft of an engine. In other cases, the lockup clutch is released to connect the input shaft of the torque converter to the output shaft of the engine.
The lockup is released to utilize a function of the torque converter thereby to achieve smooth starting, smooth accelerating or smooth speed shifting without engine knocking or stop at the time of starting, abruptly accelerating, speed shifting the vehicle.
However, in a state that a load is low and an engine rotational speed is high, the torque converter is locked up thereby to prevent loss of power due to a slip of the torque converter and hence to prevent a decrease in fuel consumption.
A cruise control unit so controls an opening of a throttle valve as to maintain a certain vehicle speed set by a driver as a desired traveling speed thereby controlling in response to a road state.
As the typical automatic transmission control to execute as described above, Japanese Utility Model Application Laid-Open 63-115558 discloses an internal combustion engine with an abnormality detector for judging an abnormality based on a rotational signal from a rotation detector for electrically detecting a rotational speed of the internal combustion engine and a fuel amount signal from a fuel amount detector for detecting a fuel supply amount to the internal combustion engine.
In the above-described internal combustion engine with the abnormality detector, it is determined that an engine rotational speed signal line is when an engine rotational speed is smaller than a predetermined value at a certain vehicle speed or more. However, even if an engine stop occurs at a certain vehicle speed or more, it is erroneously detected that the failure occurs at the engine rotational speed signal line.
In such a case, it becomes impossible to detect a failure of an ignition pulse generating an engine rotational speed detection signal to be supplied to the engine rotational speed signal line. Furthermore, there are disadvantages that the automatic transmission control based on the engine rotational speed such as, for example, a gear shift control, a lockup control, a line pressure control can not be appropriately controlled.
As the typical automatic transmission control to execute as described above, Japanese Utility Model Application Laid-Open 63-137038 discloses an automatic transmission controller in which hunting of the vehicle speed due to a gear shifting during a cruise control traveling is prevented and a fail-safe control is performed when an abnormality of an automatic transmission occurs.
More specifically, the automatic transmission controller additionally provides a memory map storing a shift schedule for controlling the automatic transmission in response to a cruise control signal supplied from a cruise controller, in which map a hysteresis width is so set as to reduce the number of repetitions of down and up shifting.
In this case, since the number of times of gear shifting during the cruise control is reduced, hunching of the vehicle speed due to the gear shifting can be prevented, and a riding comfort can be improved.
In the conventional automatic transmission controller as described above, a vehicle can be traveled smoothly without shock in the case of shifting gear during the cruise control, but it does not have a fail-safe function in case where the cruise control signal is, for example, erroneously generated even though the cruise control is not performed by the cruise controller.
Usually, the automatic transmission controller functions a gear shifting control, a lockup control, an overrunning clutch control (namely, engine brake control), etc. Therefore, if a fail-safe function is not provided, these functions are erroneously operated when a cruise control signal is erroneously generated.
In a conventional automatic transmission, for example, in a drive (D) range, an optimum gear is selected based on a vehicle speed and a throttle opening at that time, from a shift schedule map storing a predetermined shift schedule as shown in FIG. 14.
Further, in such an automatic transmission control, detection signals from various detecting sensors are input to a controller to perform a lockup control, an overrunning clutch control, a line pressure control, an auto-pattern select control, a gear shift timing control, a transfer clutch control of four-wheel drive as well as the abovedescribed gear shift control are executed.
Japanese Patent Application Laid-Open 1-145234 discloses a cruise control of a vehicle using a brake switch signal.
More specifically, as shown in FIG. 15, a detection signal SG1 from a vehicle speed sensor is input to a cruise controller 1. When a check switch 4 is turned on, a CPU 5 enters in an input waiting state of a brake switch signal SG2. When a brake pedal is once depressed and then released, the CPU 5 decides that a series of ON/OFF signals of the brake switch 3 are input. In this case, a cruise control allowance flag is set, while in case the CPU 5 decides no input of the series of signals, the CPU 5 does not set the cruise control allowance flag.
Then, whether the cruise control is requested by various switches 6 for the cruise control or not is decided. In case where the cruise control is requested, whether the cruise control allowance flag is set or not is decided, and in case the flag is set, the cruise control is executed.
In case where the cruise control allowance flag is not set, a warning light is turned on to inform the gist, and cruise control is prohibited.
Thus, in such a cruise control unit for a vehicle, an error of the brake switch 3 is checked previously by the check switch 4 for requesting a signal check of the brake switch 3 before the cruise control. Therefore, the cruise control can be reliably executed by the brake switch 3.
However, in the above-described conventional cruise control unit for a vehicle, the check switch 4 is additionally needed to check the brake switch 3, thereby causing a complicated structure.
Since the brake switch 3 is checked by the operation of the check switch 4 only before the cruise control, there is a disadvantage that the brake switch 3 cannot be checked, in case where the cruise control is not executed. Moreover, a failure of the brake switch is not executed when a braking operation is required in various running states of the vehicle such as, for example, at the time of decelerating.
Further, a shift lever for operating a range shift of an automatic transmission is connected to an inhibitor switch having a plurality of switches corresponding to the number of operating positions. When a range is selected by the operation of the shift lever, the corresponding switch generates a first level electric signal. Other switches not selected by the shift lever generate second level signals.
The positions of the shift lever includes, generally in the case of a four-speed automatic transmission, R (reverse), N (neutral), D (drive), 3 (third), 2 (second), L (low) and P (parking) of seven positions. The inhibitor switch for indicating the position of the shift lever includes seven switches each of which is closed (first level) when the corresponding position of the R, N, D, 3, 2, 1, L or P is selected by the shift lever, and opened (second level) when different positions are selected.
On the contrary, the inhibitor switch may include switches each of which opened in the case of the corresponding shift position and closed in the case of the different positions.
Therefore, any one of the seven switches is normally closed (opened) and the residual six switches are opened (closed). However, if at least one of the switches is troubled, or if an abnormality occurs at an interlocking member for operating to open or close the switch in cooperation with the shift lever, two or more switches might be simultaneously closed (opened), or all the switches might be simultaneously opened (closed). Such an abnormality causes an error in an automatic transmission control.
Switch might be, for example, instantaneously repeatedly opened/closed in an extremely short time due to a chattering when the switch is changed from open to close or vice versa. Further, in case where a mechanical member moves to sequentially close (open) one of the switches aligned in a moving direction of the mechanical member, the adjacent two switches might be simultaneously closed (opened) at a certain time point. This is normal. However, if it is conditioned to detect as an abnormality when two or more switches are simultaneously closed or all the switches are simultaneously opened, such a normal case as described above that the adjacent two switches are simultaneously closed, is erroneously determined as an abnormality.
With respect to this, Japanese Patent Application Laid-Open 63-34349 discloses a method for detecting a trouble of a gear position switch. That is, if a gear position switch does not generate an ON signal when a predetermined time is elapsed after a gear shifting is performed, it is returned to a position before the gear changing, and when the same operation as above is conducted predetermined times or more, the switch is decided to be a trouble.
However, in the above-described conventional method for detecting the trouble of the gear position switch, in case where the ON signal is not generated from the gear position switch, the gear is returned to the position before the gear shifting, and when the same operation as above is again conducted predetermined times or more, the switch is decided to be the trouble. Therefore, in the case of the trouble, it merely controls to return the position of the switch to the position before the gear shifting, and accurate automatic transmission control responsive to various traveling states of the vehicle is impossible.